Downlighters Advice wanted

I have an office with a ceiling of 4.5 m x 3.5 m and room height of 2.5 m
I would like advice on the no and rating of downlighters reqd to give a good light to work by. Also I would like to dim them if reqd and wondered if there was any particular dimmer charateristics to be aware of And does a dimmer reduce the power consumption?
Many thanks
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What sort of downlighters, halogens? My advice would be to avoid them if you are expecting normal office lighting levels. You need ridiculous numbers to get up to home lighting levels, and office lighting levels are normally much higher. Also, their colour temperature is rather low for an office.

You'll need an industrial sized dimmer if you are really going to light a room that large to office lighting standards, and possibly aircon to take the heat out of the room too.

Not by much, as they become very much less efficient when dimmed. Dimming a 500W halogen down to similar light output to a 40W lamp, and it will still be drawing something like 300W. A better way is to have several separately switched circuits, and switch some off to dim them.
Now there are downlighters designed for general lighting in offices, and these (often called "cans", particularly in the US) usually take a couple of compact fluorescent lamps. They are much bigger than the halogen downlighters of the MR16 type often used at home. They are available in dimming versions, but this is going to get expensive, as you are now talking about a product only used in rather expensive offices.
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Andrew Gabriel

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You will probably need to multiply this by another 4 or so to allow for all the general lighting coming from reflections from the floor, desktop, etc. This is where halogen downlighter efficiency is all lost; the light source is at the best end of filament lamps, but the delivery is completely wrong for general purpose lighting, and most of the light is lost into the floor.

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Andrew Gabriel

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I would not recommend downlighters for general office lighting, particularly if you will be using computers in the office. You will get a much better working light from fluorescent lights fitted with anti-glare diffusers, designed specifically for areas with computer use. If you are still using CRT screens, high-frequency fluorescents are a very good idea, but I like them anyway for the instant start and longer lamp life.
If you decide you really must have downlighters, you would do better to use them for circulation lighting and to use local task lighting to bring the workstations up to an acceptable light level. I suppose that, unless they are low energy types, one advantage of using downlighters to achieve office lighting levels is that you probably won't need to use any heating in the winter.
Colin Bignell
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What sort of downlighter do you want to use? The alternatives are broadly -
Halogen downlighters - small, but highly directional. Likely to create strong pooling of the light and to make the ceiling look dark. Ratings available from 10W to 50W. Using lots of low power ones will give a better spread of light than a smaller number of high power ones. Flood types will also give a wider spread of light than spot types. IMO the suitable only use for halogen downlighters is display lighting, or where you need a very local light.
Mirror spot reflector lamps, usually around 50-65mm diameter. Ratings available from 40W to 60W. These can be used in much the same way as halogen lamps, but they give a light that is not so strongly directional.
PAR 38 spot or flood lamps. Rather old fashioned now, but the large diameter does give a much better spread of light, particularly if you use the flood version.. Ratings available from 60W to 120W. I have used four to light a 3m x 4m kitchen.
Low energy downlighters. Usually the largest diameter fittings (the ones I have are 135mm), but they are the only lamps that do not also produce significant heat and they normally have the most diffuse spread of light. Ratings available from 9W to 35W.
Colin Bignell
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nightjar wrote:

Tbe honest I was not aware there were all these alternatives but at least now I will be able to have a meaningful conversation with the local stockists THe low energy look favorite I will need to see how they look what they cost etc
Thanks
Mike
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Not possible, halogen downlighters will never give you a decent light to work by. By their nature theyre contrasty and glarey. Theyre used for the look but are anything but ideal practical lighting. Dont worry, theyre a fashion that will pass once people wake up.
Halogen downlighting is also one of the most energy inefficient methods in current use.

Whatever light type you use, use a switchbank not dimmers. The result is: with filaments: way more energy efficient, and more reliable with fluoros: way cheaper and slightly more energy eficient
Regards, NT
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Mike Saunders wrote:

This is approx the same size as my kitchen, it's got 12 50W mains halogen downlighters. It's very bright and I might change them to 30W once it's finished. Anyone know where I can get hold of a 600W dimmer?
Cheers, Tim.
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That's 600 watts, doesn't it get hot?
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Chris Green

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CEF do a 1kW dimmer, which will fit a single back box. I just bought one yesterday.
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Frank Erskine

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